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Streptococcus pyogenes


Note gram-positive (purple) cocci in chains (arrows).


  • Streptococcus pyogenes, a group A beta streptococcus, is a Gram-positive coccus typically arranged in chains.
  • Facultative anaerobe (def).


  • Asymptomatic colonization of the upper respiratory tract in humans.


  • Pharyngitis is pread person to person primarily by respiratory droplets; skin infections are spread by direct contact with an infected person or through fomites (def).


  • The group A beta hemolytic streptococci are responsible for most acute human streptococcal infections. Between 5% and 20% of children are asymptomatic carriers. The most common infection is pharyngitis (def) with the organism usually being limited to the mucous membranes and lymphatic tissue of the upper respiratory tract. Children are at greatest risk for infection.

Clinical Disease

  • The most common infection is pharyngitis (streptococcal sore throat) with the organism usually being limited to the mucous membranes and lymphatic tissue of the upper respiratory tract. From the pharynx, however, the streptococci sometimes spread to other areas of the respiratory tract resulting in laryngitis (def), bronchitis (def), pneumonia, and otitis media (def).
  • Occasionally, it may enter the lymphatic vessels or the blood and disseminate to other areas of the body, causing septicemia (def), osteomyelitis (def), endocarditis(def), septic arthritis (def), and meningitis (def).
  • If it enters injured skin, it may cause pyogenic (def) cutaneous infections such as impetigo , erysipelas (def), orcellulitis (def).
  • Group A beta streptococcus infections can result in two autoimmune diseases (def), rheumatic fever and acute glomerulonephritis, where antibodies made against streptococcal antigens cross react with joint membranes and heart valve tissue in the case of rheumatic fever, or glomerular cells and basement membranes of the kidneys in the case of acute glomerulonephritis.
  • Certain strains of S. pyogenes cause invasive group A beta streptococcal infections. Each year in the U.S. there are between 750 and 1500 cases of necrotizing fasciitis where a streptococcal-coded protease called Exotoxin B destroys the muscle (myositis) or the muscle covering (necrotizing fasciitis). There are another 750 - 1500 cases of toxic shock-like syndrome (def) due to group A beta streptococci producing Streptococcal pyrogenic exotoxin (Spe).

From Streptococcus Group A Infections, by Sat Sharma, MD, FRCPC, FACP, FCCP, DABSM, Program Director, Associate Professor, Department of Internal Medicine, Divisions of Pulmonary and Critical Care Medicine, University of Manitoba; Site Coordinator of Respiratory Medicine, St Boniface General Hospital; and Godfrey Harding, MD, FRCPC, Program Director of Medical Microbiology, Professor, Department of Medicine, Section of Infectious Diseases and Microbiology, St Boniface Hospital, University of Manitoba, Canada.